The present invention relates to a mold clamping device in a molding device for producing molded pieces of plastic or die-cast pieces of metal.
In the field of molding machines, there exists a need for a mold clamping device of a small size and of low power requirements in to reduce the installation space and cut down the cost of energy consumed.
One conventional mold clamping device for a molding machine is illustrated in FIG. 5 of the accompanying drawings. The mold clamping device includes a guide 1, a fixed base 2, and a movable base 3 guided by the guide 1 so as to be vertically movable rectilinearly toward and away from the fixed base 2, the guide 1 and the fixed and movable bases 2, 3 being supported on a frame 4. The fixed and movable bases 2, 3 support upper and lower molds 7, 8, respectively. A toggle mechanism 5 operatively coupled between the lower base 3 and the frame 4 is driven by an actuator 6 such as a hydraulic or pneumatic cylinder 6 mounted on the frame 4.
In operation, the toggle mechanism 5 is extended by the actuator 6 to move the movable base 3 upwardly along the guide 1 until the lower mold 8 is brought into contact with the upper mold 7. As the toggle mechanism 5 is further extended, the upper and lower molds 7, 8 are clamped together under high pressure while the mold clamping mechanism including the frame 4 and the toggle mechanism 5 are being slightly deformed elastically. When the actuator 6 is operated to retract its piston rod, the toggle mechanism 5 starts to collapse to allow the upper and lower molds 7, 8 to be unclamped. Continued operation of the actuator 6 causes the toggle mechanism 5 to be folded, lowering the lower mold 8 away from the upper mold 7.
The illustrated mold clamping device is however disadvantageous for the following reasons:
(1) As the included angle between the two arms of the toggle mechanism 5 is reduced, the force with which the toggle mechanism 5 raises or lowers the movable base 3 is also reduced at a rapid rate. Since the included angle cannot therefore be smaller than a certain angle, the toggle mechanism 5 is required to be relatively tall.
(2) The rigidity of the mold clamp mechanism is reduced when the shafts of the toggle mechanism 5 are flexed and the bearing surfaces of the toggle mechanism 5 are deformed. Large forces are consequently required to drive the toggle mechanism 5.
(3) The mold clamping device consumes a large amount of energy since only the single actuator 6 is employed to carry out both the process of closing the molds 7, 8 and the process of clamping the molds 7, 8 under high pressure, these two processes imposing different loads on the actuator 6.
Another conventional mold clamping device fcr a molding machine will be described with reference to FIG. 6. The mold clamping device shown in FIG. 6 is disclosed in Japanese Laid-Open Utility Model Publication No. 56(1981)-102023. The molding machine includes a mold assembly 101 which is connected to a pair of power blocks 102 that are reciprocally movable rectilinearly in unison by a pair of slide blocks 103, respectively, that are in turn reciprocally movable rectilinearly in a direction normal to the direction of movement of the power blocks 102. The slide blocks 103 are driven by a pair of hydraulic cylinders 104, respectively.
The mold clamping device operates as follows: After the mold assembly 101 is closed, the slide blocks 103 are pulled in the direction of the arrow A by the hydraulic cylinders 104. Slanted surfaces 105 of the power blocks 102 are engaged by slanted surfaces 106 of the slide blocks 103, whereupon the mold clamp mechanism including the power and slide blocks 102, 103 are slightly deformed elastically to clamp the mold assembly 101 under a clamping force. The problems with the prior mold clamping device are that the hydraulic cylinder 104 should be large in size in proportion to the mold clamping force required, and the loss of energy is large since the mold clamping device is required to produce a force greater than the sum of a force applied to clamp the mold assembly 101 and a force applied to overcome the friction between the power and slide blocks 102, 103, but only a small force is required at an initial stage of the mold clamping cycle.